Tone compensated volume control



y 1953 s. T. KODAMA 2,637,778

TONE COMPENSATED VOLUME CONTROL Filed Oct. 20, 1950 FIG.7

INVEN TOR. GEORGE T KDDAMA FIG. 6

May 5, 1953 G. T. KODAMA 7 TONE COMPENSATED VOLUME CONTROL Filed Oct. 20, 1950 2 SHEETS-SHEET 2 INPUT SIGNAL MODULATION OUTPUT I N V EN TOR. GEO/P65 I/KQOAMA Patented May 5, 1953 "TONE 'COMPENS AITEDVOL UME CONTROL George..T..K6dama;LDunstable,aMass., ias'signor: to .Sptague Electric Company, .North ;Adams,

--Mass., a corporation of...Massachusctts Application October 20, I950,ISerial No; 191,108

This :invention relates to tone-compensated.

volume controls,- and moreparticularly to'such 'volume. controls for :signal reproducing systems :asuch as thoseusedin radio andtelevision-rc- :ceivers and sound-record repro'ducers.

.=Thercharacteristics of the human car are such athat the apparentiloudness of low freguency itones'relative-to middle andhigh-"frequnecy tones 311801163585 as the absolute signal intensity is-reduced. In 1 order to compensate for I this effect,

:volume controlsare sometimes arranged-so'that the'volumecontrol reduces the audible signal output, the reductionin the higher frequency :range is moreflthan' that of the low-frequencies. :ESuch .volume: controls are known as tone-compensated volume controls and are also desirable ;:because they give better results in locations having poor acoustic characteristics; andtheyrcduce Ethe effects of hiss, scratch, or the otherhighfrcnuency noise in'the output of sound reproducers Etc-which they are attached. In fact practically allquality radio and television receivers-are pro- -vided-with tone-compensated volume'controls.

. .xAlthough tone c'ompensated 'volume :control .vcircuits are well" known and of proven" merit; the :cost of such-circuits has been excessive, by reason of the large number "of resistors and capacitors inexpensive tomake-and incorporated in stand- :ard equipment. Further obj ects 'willabecome' ob- .vious' from the description and claims that follow.

.The present invention -provides an integral tone-compensated volume control. The control includes circuit elements produced in accordance vwith printed electronic circuit techniques, andis of compact, inexpensive construction.

The invention'will be more fully described with .referenceto the. appended drawings wherein:

Fig. 1 isia sectionalview of one embodiment-of the toneecompensated volume'controlzof the invention, taken along line ll :of' Fig. .2;

Fig. 2 is a transversezsection alonglineL-Z of the construction 'of Fig. 1;

'Fig. 3 isa plan view-of the statorrelementof the'construction of'Figsrl and 2;

Fig. 4 is a plan view of the opposite face of the stator element shown in Fig. ,-,3;

Fig 5 is a sectional-view. taken'along line -5--5 of Fig. 3;

czFig.5.6 is asectional-view similar to Fig. 5 of'an :1Claims. (Cl.=17844) -alternative stator structure in accordance with the invention;

-Fig."'7 is-a plan-view of the rotor member used in 'the embodiment ofthe invention shown in =Fig.fll;-

"Fig. 8 is-airagmentary diagram-of a portion of a: radio receiver circuit showing the -tone-co'mpensatedvolume control circuit-in which the "control of the invention can be used;

*Figs. 9 and 10 are fragmentary :plan views similarto- Figs. 3- and 4 of -a"modified stator memher-zcxemplifyingi the invention; and

"Figi-lliis awplanvievv similar to-Fig. 3 of a iurthe! type of stator: member embodying the 'pres- '15 invention. Referringparticularly to Figs. I 1 and '2; a substantially: circular dielectric plate I 3 with an ex- 'inner'end B -outwardly against a ledge-fl in the portiomofthc platelboundingthe aperture. The hushing is externally threaded to receive nut (not =sh'o=wn) by which" the entire structure may hemounted on -'a support (not shown) in the conventionalmanner.

. A flatceramic-idisci23,-.the faces of which carry athezprinted:to-nescompensated circuit (see' Figs. 72-11) :isamountedron oneside'of .the'rplate l 3. The: nature; Of'i the-printed; circuit structure will the (particularly described 1 with reference to the vszuitablefigures. .lDi'sc 23 WhiGhLiSiIl the shape of :.a; ring, is :fitted over-a fiange "33 which projects up from around the bushing aperture.

xAzconducting contact :ring 38 is l held on the eflangei33 concentrically'withthe-bushing [E and :has arradial armc3l interlocked inwa'slot in diwelectric; extension l-t to keep the ring in position. notch l.9.in,ceramic-. disc. 23. is engaged ib-y :arm .--3'l,,and.;aretaining. nib on 28. can: be. formed the arm .to. clamp the ring against the 1 flange 33. The ringanditsarm '3? ,form one"v terminal .for the volumecontrol member.

Arotor member comprises a. shaft. rotatably fitted through bushing 15 and having a .split and/orsp-lined outer end as is usualforreceivmid-point to slidably engage a suitable portion of the circuit on the ceramic ring 23. The contact elements press against the surfaces they engage, and urge the shaft 40 to the right as seen in Fig. 1, but such movement of the shaft is prevented by a split snap ring 49 held in a groove in the shaft and engaging a washer 55 between it and the bushing.

The printed circuit element 23, as shown in Figs. 1-5 is shown as a coated high dielectric constant ceramic disk 24 having a central aperture therein. As shown in Figs. 2 and 3, one face 34 of disk 24 has spaced conductive coatings 50 radially distributed thereon. The coatings are metallic (generally silver) and are formed on and bonded with the dielectric by any suitable method such as those described in National Bureau of Standards Circular 468 entitled Printed Circuit Techniques, particularly pages 5 to 14. A portion of these coatings together with an adjacent annular sector of dielectric disk 24 is covered with an enamel layer 52 along the outer portions of which is disposed a sector'of an annularly shaped electrically resistive coating 54. Such a resistive coating can also be applied in any suitable manner such as those described in the abovementioned circular, particularly pages 5 to 16. The individual conductive coatings 50 are separately electrically connected to spaced portions of-resistive coating 54 by means of resistive coating strips 5| which extend from arcuate coating 54 over enamel 52. Resistive coating strip 5| can be of the same or different composition as resistor element 54, if desired, and can be painted or printed upon the ceramic, enamel or metallic coatings at the same time or in successive steps. Metallic terminal coatings 60, 6| (see Fig. 3), preferably of silver, are applied over the ends of resistor element 54 and extend over and upon the other face of printed circuit element 23.

This other face 35 as shown in Figs. 4 and 5 has a metallic coating 64 similar in composition to coatings and in capacitive relationship therewith. One end of resistive coating 54 and the corresponding end of conductive coating 64 are electrically connected by means of terminal coating 9| as shown in Fig. 4, while the other ends of these coatings are left unconnected. The terminal coatings 60, 6| on face 35 are separately held against conductive terminal strips 21, 28

fastened to dielectric extension I 4 as by eyelets 9!, 32. An additional spring-like nib or kinked portion 39 of member 31 tends to compressively retain printed circuit element 23 against dielectric plate l3.

A modification of the above structure is shown in Fig. 6. Here a resistive coating 14 takes the place of coatings 50, 5|, 52 and 54 and acts both as a resistor element and as a series of capacitor plates for capacitive cooperation with conductive coating 84. If desired the coating 14 may have individual capacitive portions directly opposite coating 64 separated from each other and connected by radially extending interconnected arms to more closely duplicate the structure of Fig. 3. In either modification contact knob 48 provides a slidable electrical contact with resistor element 54 or the non-capacitive, outer extremity, of resistor-capacitor element 1'4 and connects through contact member 45 to fixed contact ring 36. By moving contact knob 48 over the surface of resistor element 54 or resistor-capacitor element 14 it is possible to tap off part of the resistor capacitor-circuit and thus to supply varying portions of the signal voltage appearing between the ends of resistive coating 54.

The volume controls of the present invention are preferably enclosed in a casing or cover 51 having ears 58 which, as shown in Fig. 1, may be bent over and engaged against a metallic plate 59 held between dielectric plate l3 and bushing I6. The plate 59 may be held against rotation as by a non-circular central aperture engaging a correspondingly shaped portion of the bushing. A notch may also be provided in plate 59 for receiving each ear 58 to prevent rotation of the casing. The enclosed parts are thus protected from damage and shielded against interfering electrical and/or magnetic disturbances.

The diagram shown in Fig. 8 illustrates a manner for using the volume control of the present invention in the circuit of a standard type of radio receiver. The input signal is received in the primary of transformer the secondary of which is tuned to the intermediate or heterodyne frequency by means of capacitor 8|. This intermediate frequency signal which is modulated by audio signals at a much lower frequency is then demodulated by means of grounded diode detector 83 connected to one lead of the transformers secondary winding. The modulated signal then passes through the filter network 9|, 92, 93 to the load resistor from which it is capacitively coupled to the tone-compensated volume control of Fig. l. The circuit elements are numbered to correspond with the previously described structures. The modulated output frequency is fed from the tone-compensated volume control tap 48 toan audio amplifier stage. Both the radio and tone-compensated volume control circuits are well known to the art and they will not be discussed further except to say that with load resistors having an impedance of /2 to2 megohms, the resistive coating 84 can have a corresponding impedance, the resistive links 5| about one-tenth that impedance, and the individual capacitors 50-54 may use a bariumstrontium titanate disc having 15 to 25% barium titanate and about 12 to 18 thousandths of an inch thick, with an effective electrode area of about 0.1 to 0.3 square centimeter. Figs. 9 and 10 show a modified form of volum control according to this invention wherein many of the circuit elements of Fig. 8 are integrally incorporated by adding conductive coatings 94, I02 and resistor strip 92, 95 to face 55 of printed circuit element 23, and conductive coating IUI to the other face 34. Capacitance 5! is provided by edge effect between adjacent coatings 64, 94. Resistor strip 92, 95 provides the resistances shown. Capacitance 93 is provided by edge effect between coating l 62, and the terminal SI of coating 64, and the coupling capacitor is provided by means of opposed coatings IEH, M12. The edge effect capacitances can be increased or decreased by suitable modification of the coatings. Thus by increasing the, length of coating 94, capacitance 9| can be readily increased. Correspondingly, of the coating terminal 5| and coating I02 forming capacitor 93, either can be provided with extensions positioned closely adjacent the other to increase the capacitance. The one not extended can be shortened somewhat to make more room for the extension. Circuit connedtions are completed by contact of terminal strips 27, 28 with coatings 94, 6| respectively.

The remainder of the volume control can be as shown in connection with either Figs. 3 or 7. Fig. 11 is a further exemplification of the in- .with ..coatin gs I58.

vention .in .which .the separate :capacitor .electrodes 'I ,are located radiallyi outside :oii'fthe resistiveccoating [54, and .the, resistivev linkstfil Links l5! canaccordreadily; applied .as ,by the .conventional silkscreening technique described the abover-identified, circular.

.In ,this construction, the ppposing groundsreturncoating ontthe other facebf the disciis at the peripheral portion of the:-.disc.aligned ,The terminals-bf resistive coating .154 are shownrat, I52, 153,-.coating I53 being continued over..toythereversejace where itnbecomes. ground returnterminalil ,asin Fig.

4. Terminal I 52 does not continue over totthe votheriacebut is incapacitive .relationlwith a "correspondingly positioned, coating ,(not.;shown) on that other face to provide an inputcapacitance as-shown at till, H32 in Figs-8. This modification of the invention can abeusedwitha sepavrate load resistor.corresponding to resistor :95

ofgEig. 8.

To further lengthen theresistive strips I5l. they can be shifted so that they extend from the' outer margins of'the individual capacitor electrodes I59 between .the, individual capacitors to the section i5 3.

Ii desiredthe dielectric disc can be of solid ratherthan annular construction, as byrmerely arrangingthe disc on the opposite side=of.-the :inner ,end .of rotor shaft1-.4ll,.with thecontact knob .148 correspondingly, relocated. This 113E0- videseven more room onwhichthe individual capacitorcelectrodes 5U andJBUUcan bencarr-ied. In addition, a solid disc is somewhat simpler to manufacture than the annular or ring shaped one shown in Fig. 3.

The integral tone compensated volume control unit of the present invention need not be used only in circuits of the type shown in Fig. 8 above. Thus for example filter capacitor 9| can be omitted, and if desired the entire filter network 9!, 92, 93 need not be used. According to further modifications the load resistor 95 can also be omitted, in which case the direct current circuit of diode 83 should be completed as by shifting capacitor IDI, I02 from the volume control input line to the output line connected to tap 48. This latter type of construction can be conveniently embodied in the integral unit of the invention as by severing lead arm 31 and overlapping the severed ends in capacitive relationship on opposite sides of a dielectric such as plate 13. Alternatively contact ring 38 can be replaced by a correspondingly positioned coating on ceramic disc 24, this coating being capacitively aligned with a coating on the opposite face of the disc which opposite coating can be mechanically engaged with a fixed contact strip similar to those shown at 21 and 2a.

Briefly, the tone-compensated volume control operates as follows. As the volume is lowered by tapping the desired signal on a shorter length of resistor element 54, the capacitances 5|], 64 effectively become larger portions of the signal load provided by the resistors 54, 4| and these capacitors. At the lower frequencies these capacitors are of little effect but the higher frequencies are appreciably attenuated. Thus as thervolumei-control;reduces;theggain, therreduc- 5 111011, is-. -1ess ior -1ower. frG uencies-than torzhigher frequencies.

The .requi-redwvalues :of resistance and :capaci- :;.tance .of ,thevtone-compensated pvolume -';control ecircuitarermerely ..a. matter of designeand :may -be varied .fromxthose given: above by= changing .the relative dimensions, the ,re1ative,;position s,"or the ecompositionof -.the ceramic, as ,well ,as ;.the ,especific; resistivity of.- the conductive and resistive ,pcoatings.

.:As..manyapparently :widely dilferent embodiementaofr this invention maybeumadeswithout departing from ithe spirit-Tand scope .hereot, ita-l8 to be. understood thatithis; invention isnot limited .to the speci fic gembodiments hereof except :as defined ,intthe ap ended.- claims.

ltwhatisaclaimed is:

:1.,iI-n atone compensated volume control: ca .eeramicdEc-havingon one face an elongatedar- .cuatelyashaped resistive coating extending more than-halfway aroundthis face-and a plurality of separate. electrically; conductive coating portions spaced. from but, separately resistivelyconnected to portions of the resistive coating and-ionthe other iace of the discan integralelectrically con- ..ductive ,coating ineffective. capacitive -,relationship -vwithall the. spacedicoatings, apair .of fixed contact pmembers separately connected to each ,end of said resistive. coating, .oneof saidfixedicontact :members being -.a1so- .c0nnected to saidlintegral'. conductive K coating and a pivoted contact tmember physically movable into electrical: con- .nection with anydesired, portion. of ,said resistive -.coating.

2.. In v,a tone-compensated volume-control: a rin -shaped ceramic disc-havingon oneface-.an ,.arcuate1y shaped i-ielectrically resistive locating, .spaced capacitor electrode coating radiallyedis- ,placcdirom. but: separately.-v resistively connected to spaced portions of the resistive coating, and on its other face an arcuately shaped capacitor electrode coating in effective capacitive relationship with the spaced electrode coatings; fixed contact members separately connected to the ends of said resistive coating one of the fixed contact members being also electrically connected to said arcuately shaped capacitor electrode coating, a. rotor structure extendin through said ceramic ring and having a movable contact member elec trically connected to wipingly engage said resistor strip; and fixed electrical terminal elements separately connected to all of said contact members.

3. In a tone-compensated volume control: a ring-shaped ceramic disc having arcuately disposed around one face a series of spaced capacitor electrode coatings, an annular insulating coating layer covering at least a portion of each electrode coating, an elongated arcuate electrically resistive coating radially spaced resistive coating elements from the series of electrode coatings on the insulating layer and electrically connecting said spaced capacitor electrode coatings separately to spaced portions of the arcuate resistive coating and on the other face of the disc an arcuately shaped capacitor electrode coating in eifective capacitive relationship with the spaced electrode coating; fixed contact members separately connected to the ends of said resistive coating one of the fixed contact members being also electrically connected to said arcuately shaped capacitor electrode coating, a rotor structure extending through said ceramic ring and having a movable contact member electrically connected to wipingly engage said resistor strip; and fixed electrical terminal elements separately connected to all of said contact members.

4. In a tone-compensating volume control unit for supplying any portion of an incoming signal and automatically compensating the supplied portion against the variation in the tonal emphasis of the human ear with respect to intensity; a disc of high dielectric constant alkaline earth titanate ceramic, an elongated wide electrically resistive coating on one surface of the disc, an elongated electrically conductive coating on the other surface of the disc and overlapping only a portion of the width Of the resistive coating to establish a corresponding distributed capacitance, a movable contact top held for selectable engagement with limited portions of an elongated section of the resistive coating spaced from the overlapped portion to insert resistive connections between the tapped Width of the resistive coating and the distributed capacitance, and a pair of terminals connected to the respective ends of the resistive coating, one of said terminals being also connected to the conductive coating.

5. In a tone-compensating volume control: a dielectric base plate having on its opposite faces a row of pairs of opposed electrode coatings each pair forming a separate capacitance unit, the electrodes on one face being conductively connected in common, and the electrodes of the other face being resistively connected by resistive coating portions to spaced portions of a continuous elongated resistive base plate coating spaced from the capacitor units, a first fixed terminal member electrically connected to one end of said resistive coating, a second fixed terminal member electrically connected to the other end of said resistive coating and to the common capacitor electrodes, and a movable contact member electrically connected to and physically movable along said resistive coating to provide an adjustable tone-compensated volume controlling potentiometer tap for signals carried by the resistive coating.

6. The combination as defined by claim 5 in which the base plate includes additional coatings connected to form a high frequency by-passing filter assembly and a signal supply capacitance both in series with the elongated resistive coating, and a load resistor in parallel to the elongated resistive coating.

7. The combination of claim 5 in which the capacitor electrodes opposing the common electrode are sections of the electrically resistive coating portions. 7

8. The combination of claim 5 in which the capacitor electrodes opposing the common electrode are electrically conductive coatings different from the electrically resistive coating portions.

9. The combination of claim 5 in which the base plate includes additional coating elements connected to form a high frequency by-passing filter connected to the first fixed terminal.

10. The combination of claim 5 in which the base plate includes additional coating elements connected to form a coupling capacitor connected to the first fixed terminal.

GEORGE T. KODAMA.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,037,735 Holst Apr. 21, 1936 2,121,091 Maginnis June 21, 1938 2,464,377 Cohen et al Mar. 15, 1949 2,474,988 Sargrove July 5, 1949 2,523,856 Baker Sept. 26, 1950 

